1. Field of the Invention
The present invention relates to a liquid ejection device and an image forming apparatus, and more specifically to an ejection abnormality compensation technology for detecting and compensating ejection abnormalities in the nozzles of an ejection head.
2. Description of the Related Art
In recent years, inkjet printers have come to be used widely as data output apparatuses for outputting images, documents, or the like. By driving recording elements, such as nozzles, provided in a recording head in accordance with data, an inkjet printer is able to form data onto a recording medium, such as recording paper by means of ink ejected from the nozzles.
An inkjet printer forms an image on recording paper by causing a recording head having a plurality of nozzles and a recording medium to move relatively to each other, while causing ink droplets to be ejected from the nozzles. If an ejection abnormality occurs for some reason in a portion of these nozzles, then a fault occurs in the resulting image, thereby causing image quality to decline. Therefore, it is necessary to take countermeasures.
Conventional methods for detecting ejection abnormalities at nozzles include a method in which a test pattern or an actual image is printed and ejection abnormalities are detected from the resulting image, and a method in which the ejection characteristics are measured inside the recording head. Furthermore, if an ejection abnormality is detected by one of these methods, then droplet ejection control is implemented in order to prevent image faults, for instance, compensatory ejection is performed in such a manner that larger dots than normal are formed by adjacent nozzles in place of the nozzle having an ejection abnormality, or compensatory ejection is performed by driving complementary nozzles, if the recording head is provided with complementary nozzles.
Japanese Patent Application Publication No. 2001-63008 discloses a recording apparatus, control method for same and computer-readable memory, in which data on defective recording elements is stored, complementary elements are chosen according to the data thus stored, and recording is performed by the complementary elements chosen in the defective elements stead.
Japanese Patent Application Publication No. 2001-315318 discloses an inkjet recording apparatus and inkjet recording method, in which non-ejecting nozzles are detected and the amounts ejected from nozzles adjacent to the non-ejecting nozzles are adjusted.
However, in a method where print results, such as a test pattern or an actual image, are determined, it is necessary to eject ink onto the recording medium, and hence recording medium and ink are consumed wastefully for the purpose of determination. Moreover, in a method where physical properties are measured inside the recording head, although it is possible to accurately identify nozzles having an ejection abnormality, it is difficult to determine the extent of the ejection abnormality.
Moreover, if complementary nozzles are provided, then space for installing these complementary nozzles is required, and hence there is a problem in that the head becomes large in size.
The recording apparatus and control method for same described in Japanese Patent Application Publication No. 2001-63008 requires recording actually to be performed in order to identify defective recording elements, and hence it does not resolve the problem of recording media and ink being used wastefully. Furthermore, in order to identify recording elements which become defective over the passage of time, it is necessary to identify defective recording elements periodically and to register these defective recording elements.
Moreover, in the inkjet recording apparatus and the inkjet recording method according to Japanese Patent Application Publication No. 2001-315318, since a defective nozzle is compensated for by changing the amount of ink ejected by the nozzles adjacent to the defective nozzle, it is necessary to change the ejection algorithm (ejection control) accordingly, and hence the burden on the ejection control system becomes very large.